Distribution Category:

Coal Conversion and Utilization--

Coal Gasification (UC-90c)

ANL-78-43

ARGONNE NATIONAL LABORATORY

9700 South Cass AvenueArgonne, Illinois 60439

GAMMA RADIOGRAPH', OF REFRACTORY-LINEDVESSELS AND COMPONENTS

by

N. P. Lapinski

Materials Science Division

August 1978

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3

TABLE OF CONTENTS

Page

ABSTRACT.......... .... ... . .................. ..

1. INTRODUCTION ...... .....................

II. LITERATURE REVIEW AND LABORATORY TESTS. . . . . . . .

111. FIELD TESTS AND RESULTS. . . . . . . . . . . . . . . . . . . . . . .

IV. GAMMA-RADIOGRAPHIC PROCEDURES FOR FIELD TESTS. .

A. Equipment and Field-implementation Considerations. . ..

B. Single-wall Radiography . . . . . . . . . . . . . . . . . . . . . . . .

C. Double-wall Radiography . . . . . . . . . . . . . . . . . . . . . . .

D. Conclusions and Recommendations . . . . . . . . . . . . . . . . .

APPENDIX: Supplementary Information Related to Radioisotopic

Sources ......................................

1. Radiographic Sources . . . . . . . . . . . . . . . . . . . .

2. Fundamentals of Radiography. . . . . . . . . . . . . .

3. Radiation Safety. . . . . . . . . . . . . . . . . . . . . . . .

4. Measuring and Monitoring Devices . . . . . . . . . . .

ACKNOWLEDGMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

REFERENCES ....................................

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4

LIST OF FIGURES

No. Title Page

1. Cross Section of Part of Bi-Gas Gasifier Vessel ... . . ... . ... 7

2. Cross Section of Combustor Vessel at Battelle . . .. . . .. . ... . 8

3. Schematic of Bypass Line at Battelle .. . . . . . . . . . . . . . . . .. . 8

4. Radiograph of Section of Battelle's Combustor Vessel ShowingVoids beneath Vapor Barrier and Orientation of a Hanger ... .. . 12

5. Radiograph of Section of Bi-Gas Gasifier Showing Void in Centerof Film .. .. . ... . .... . .. . ..... .. .. .. .. .. .. . ... . 13

6. Schematic Diagram of Refractory-lined Transfer Line at

Battelle .............................................. 13

7. Schematic Diagram of Y Section before Solids Were Circulatedthrough System . . . . . . . . . . . . .. . .. . . . . . . . . . . .. . . . . . 13

8. Schematic Diagram of Y Section after Solids Were Circulatedthrough System . . . . . . . . .. . .. .. . . .. ... . .. . . .. . .. . . 14

9. Schematic Diagram of Elbow before Solids Were Circulatedthrough System . . . .. . . . . ... . .. .. .. ... . ... . .. . . . . . 14

10. Schematic Diagram of Elbow Showing Refractory Erosion afterSolids Were Circulated through System .. . . .. . .. . . .. . . .. . 15

11. Vessel Photographed from Above, Indicating Location of HollowTube as Secured to the Flange . .. . . . . . . . ... . . .. .. . . .. . 16

12. Disk-shaped Penetrameter of Type Presently in Use . . .. . . . . . 17

13. Photograph of Gasifier Vessel Showing Position of FilmCassettes Secured to Vessel . . ... . ... . ...... . ... ... . . 18

14. Proposed Film-identification Method for Panoramic Radiographyof Refractory-lined Vessel . . . .. . . .. .. . . .. . . .... ... . . 18

15. Typical Arrangement for Radiographing Refractory-lined Pipingto Obtain Bore Contour . . .. . . ..... ...... .. ...... . . . . 20

16. Photograph of Collimator in Position to Generate Radiograph . . . 20

17. Decay Chart for 60Co .. . ... ... .... . ... ..... . . . . ... .. 22

18. Schematic Diagram Showing Fundamentals of RadiographicExposure....... ................................ 24

5

LIST OF TABLES

No. Title Page

I. Physical Properties of Refractories after Curing . . . .. . . . . . . i1

II. Half-value Layers for 60Co Radiation of Some Common Materialsin Coal-conversion Systems. . . . . . . . . . .. .. . . .. . . . . . . .. . 16

III. Total Amount of 6 0Co Radiation Required to Yield Various FilmD ensities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . 19

7

GAMMA RADIOGRAPHY OF REFRACTORY -LINEDVESSELS AND COMPONENTS

by

N. P. Lapinski

ABSTRACT

Materials used in coal-conversion systems are exposedto high pressure, high temperature, corrosive and erosivegases, and liquids containing particulate matter. These severe

environments necessitate an assessment of the integrity of

components to prevent premature failures. Gamma radiography

was evaluated as a viable technique for testing s compo-

nents in the laboratory or after operation in situ. Penetrameters

(image-quality indicators)were developed for refractory-lined

vessels and transfer lines, and exposure times for various com -

binations of refractory-steel thicknesses were determined.Radiography with bOCo va s pe rformed on ga sifier vessels, com -bustor vessels, and critical transfer lines in existing pilotplants using the experience gained through laboratory experi-

ments. The results show that gamma radiography is a prac-tical and effective method to detect critical conditions in coal-conversion system components.

' INTRODUCTION

Prevention of premature materials failure in coal-conversion compo-nents necessitates an assessment of the integrity of the refractory before andduring plant operation. Gamma radiography seemed to be an especially suit-able method for examining laminated structures such as refractory-lined gas-ification vessels and transfc - lines (see Figs. 1 -3).

3.76 tm 00. 321cm 0SA 213122 WATER COOLANT CENTERLIETUBES o

C^ D - 2 to E iHg. 1

- Cros, Section of Part of Oi-Gas Gas-

- r ,ifier Vessel. Neg. No. MSI-65122.

P 46 to -

AL*RA1 U S?

.95 cm

E

-1.9 cm-a

KAOTABREFRACTORY

-- 46 cm --

CENTERLINEOF

COMBUSTOR

Do 000 0 000000 00 0 00 0

Sp 0 X0 0 '0 O0C 0~ 00 0 00

0

n p 00 0 0

0 0p 0 0 00 0 0000o p oo0000 000 0 00

o 0 0 00So0O % op, 0 0

D o 0 % Do

00004~ 0 7000 08

7.6 cm -23 cm-

Fig. 3

Schematic of Bypass Line atBattelle. Neg. No. MD-65121.

36 cm '0 0

ODD%^ D0 O B

p~ 006 co 0 0

T10cm

,0o o 0O0 e 0

// // // // // //0

Before going into details concerning some experimental radiography

conducted on mockups in the laboratory and on actual gasification-plant compo-nents, we will review some basic characteristics of X- and gamma radiation.

X rays and gamma rays"2 z are forms of electromagnetic radiation, as arevisible light, ultraviolet light, infrared waves, radio waves, and cosmic rays.

The wavelength region of the electromagnetic spectrum covered by X - andgamma radiation is not absolutely defined, but for our present purpose, wewill consider the wavelength range from 0.001 to 1000 A (1 angstrom = 10-10 m).The general properties of X and gamma rays may be summarized as follows.

1. Invisible and pass through space without transference of matter.

2. Propagate in straight lines.

3. Not affected by electric or magnetic fields.

4. Evidenced on photographic film by density.

5. Capable of ionizing gases.

6. Differentially absorbed by all media.

7. Able to damage or kill living cells and to produce genetic mutations.

Many of these properties apply to radiography, the most useful beingfilm blackening, straight-line propagation, and differential absorption inmatter.

8

Fig. 2

Cross Section of Combustor Vesselat Battelle. Neg. No. MSD-65123.

9

Gamma radiation, unlike X-radiation, is nuclear in origin. Only a few

radioisotopes decay by simple emission of gamma radiation. Usually, gamma

emission occurs after the nucleus emits alpha or beta rays. Since gamma rays

have neither charge nor appreciable mass, the isotope remains unchanged after

the emission of gamma radiation; only the available energy is reduced, leaving

the product nucleus in a more stable state. Gamma-ray energies are charac-

teristic of particular isotopes. The energies vary widely, from a few thousand

electron volts (keV) to several million electron volts (MeV).

Important definitions related to radioisotopic sources are listed in

the appendix.

II. LITERATURE REVIEW AND LABORATORY TESTS

Two literature searches were conducted to assess the applicability ofradiography to ceramic-lined steel structures, and to determine the current

state of the art. Key words used in these searches included: gamma radiog-

raphy of refractories, X-ray radiography of refractories, refractory-lined

vessels, refractory, piping, nondestructive testing, and nondestructive evalu-

ation of refractories and ceramics. The search yielded only two articles in

addition to ANL Quarterly Reports. In his article, 3 Schackelford presents a

nomograph to calculate parameters for radiography of refractories. The

accompanying text only explains the use of the nomograph. Borbas et al. 4 in

their paper describe the application of gamma-radiation absorption techniques

to measure the density of refractories.

Results of this search indicated the need for laboratory tests of

ceramic-steel composites and the development of penetrameters (image-

quality indicators). 5 -9 A 1.2 x 1.27-m (48 x 50-in.) full-scale mockup of the

refractory/steel laminate cross section of the Battelle-Columbus gasifier

[228-mm (9-in.) refractory, 6.35-mm (0.75-in.) steel] was assembled to eval-uate the crack-detection capability of gamma radiography with refractories ofsuch a layered structure. Gamma radiographs of the mockup were generated

after the refractory had air-dried for 5 days. The entire casting was divided

for crack mapping into four quadrants, each separately radiographed on four

35.6 x 43.2-cm (14 x 17-in.) sheets of Eastman Kodak Type AA film. Thesource-to-film distance of 1.2 m (48 in.) required an exposure time of 5 h

when a 2.22 x 10 1 -Bq (6-Ci) 6OCo source was used. The radiographs revealedinternal cracks, which varied in length from 7.7 to 28 cm (3 to 10.5 in.) and inwidth from 1.58 to 4.75 mm (0.062 to 0.187 in.). These cracks did not coincidewith numerous visible surface cracks.

A second set of radiographs was taken after the mockup was fired andthermally cycled. The radiographs revealed that curing increased the numberand size of cracks. Refractory moisture content was not a significant factorin obtaining good radiographs. The averapa difference in photographic densitybetween radiographs taken shortly after the refractory was poured and thosetaken after curing was only '0.41.

10

At the same time, radiographic experiments were conducted to relatethe film density to refractory thickness and to determine the spatial resolu-tion limits. The refractory used was high-density alumina into which 6.25-mm(0.25-in.)-wide slots were cut. The slotted refractory was placed on 65.6-mm(2.625-in.) steel plate, and supplementary molded refractories were added tocomplete the mockup of the cross section of a typical air-cooled pilot-plant

gasifier jacket. A steel step wedge was placed adjacent to the mockup, andradiographs were taken. From these radiographs, the relationship between

the film density and the refractory wall thickness was established",6 and nor-

malized. This relationship indicated that refractory thickness could be deter-

mined to 6.3 mm (0.25 in.), using normalized film densities.

Additional studies on the sensitivity of film density to refractory-thickness reduction have been conducted using a step wedge with 15 steps

[6.3 mm (0.25 in.) deep by 12.5 mm (0.5 in.) wide], cut from a high-densityaluminum oxide molded refractory. A densitometer was used to determine

film density at each reduced thickness. The results were similar to those

obtained with the slotted samples, indicating that refractory-thickness reduc-

tion can easily be measured by gamma radiography if a calibration is avail-

able to allow the film density to be related to thickness.

To quantitatively determine the resolution of radiographs, penetrame-

ters had to be developed. The penetrameters, constructed from Norton 4190

Alundurn refractory, were 11.4 cm (4.5 in.) long, 6.3 cm (2.5 in.) wide, and

6.35 mm (0.25 in.) thick. The penetrameters had through-hole diameters of

t/2, it, 2t, and 3t (t equals the penetrameter thickness). Laboratory testswere conducted to compare the placement of penetrameters on both the source

and film side of a refractory/steel laminate mockup. The refractory/steel

mockup consisted of 28 cm (11 in.) of KAOTAB refractory and 6.7 cm (2.75 in.)

of steel. The gamma radiographs indicated that placement of the penetrameter

on the film side is preferable to placement on the source side, because in theformer case all the holes can be seen in the penetrameter, whereas in the latter

case only the 3t and 2t holes can be discerned. This is due to the large distancerequired between the object, penetrameter, and film when the penetrarneter is

placed on the source side in the conventional manner. This large distance de-

grades the image.

Disk-type penetrameters were also developed and fabricated from high-density refractory. They were 2.54 cm (1 in.) in diameter and 0.635 cm(0.25 in.) thick, with a 1.27-cm (0.5-in.)-dia through-hole in the center. Thedisk-type penetrameters were constructed especially for use in radiography of

refractory/steel laminated components.

III. FIELD TESTS AND RESULTS

Field gamma radiography was performed on the gasifier vessel atBi-Gas, and on the combustor vessel and transfer lines at Battelle. These

11

tests were conducted to establish exposure parameters, assess field-implementation difficulties and requirements, and develop methods to obtainpanoramic gamma radiographs. All the radiographed components had a re-fractory lining.

Refractories that are common in coal-conversion systems includeCastolast G, KAOTAB, ALFRAX 101 ALFRAX BI 57, and ALFRAX BI. Ta-ble I lists the manufacturers' stated physical properties for these refractoriesafter curing. Severe environments such as high temperature, high pressure,and thermal cycling can cause degradation and cracking of these refractories.

Refract(

Castolabt

TABLE I. Physica. Properties of Refractoris_ after it during

Aluminad MaximumContent, Dens.' Service

ory Manufacturer % kg /r 'ii perature, C

G lHarbison-Walker 97.7 2610 1815Refractories

KAOTAB Babcock and Wilcox 95 2659 1815

ALFRAX 101 Carborundum,, 99 45 2980 1870

ALFRAX BI 57 Carborundum 94.6 1460 1815

ALFRAX BI Carborundum 78.80 1398 17601881-4

aA LOp

Schematic diagrams of pressure-vessel cross sections are shown inFigs. 1 and 2. Figure 1, a cross section of the Bi-Gas gasifier vessel, rep-resents the thickest section thus far radiographed. The 9.04-cm (3.562-in.)

steel shell (SA-3870) is circumferentially lined with 3.76-cm (1.5-in.)-OD,3.29-cm (1.297-in.)-ID steel (SA 213T22) water-coolant tubes, which are in-sulated with 46 cm (18 in.) of ALFRAX BI 57 and an inner layer of precuredALFRAX 101 brick 11.43 cm (4.5 in.) thick, bet in place with ALFRAX 3449mortar.

The cross section in Fig. 2 is of the combustor vessel at Battelle. The1.9-cm (0.75-in.) steel (SA-A3870) shell is lined with 23 cm (9 in.) of a mono-lithic high-density refractory (KAOTAB). At intervals of 61 cm (24 in.), vaporbarriers are installed around the circumference of the steel vessel to attenu-ate gas flow should the refractory crack. Part of a refractory-lined transferline is shown in Fig. 3. This is a 35.5-cm (14-in.)-OD Schedule 20 steel pipelined with 23 cm (9 in.) of KAOTAB refractory with a 10-cm (4-in.) bore.

During the field test, a 6Co source was used and a technique was de-veloped for obtaining useful radiographs. The procedures, described inSec. IV,can serve as a reference for future gamma-radiographic inspections of linedcoal-conversion plant components. The techniques permit one to obtain gammaradiographs of refractory-lined vessels and piping to show possible discontinu-ities in the refractory, anchor orientation, and bore definition.

12

An example of a gamma radiograph showing anchor orientation and

air pockets beneath a vapor barrier is shown in Fig. 4. (See Fig. 2 for the

cross section.) The voids, typically 3.8-7.6 mm (0.149-0.299 in.) long and1.3-2.5 mm (0.051-0.098 in.) wide, were discernible in each radiographed ele-

vation. Figure 5, a radiograph of part of the Bi-Gas vessel (see Fig. 3 for thecross section), shows a typical void at the center. The discontinuity is 23 cm

(9 in.) long and 0.64-1.6 cm (0.251-0.625 in.) wide. The clarity of the coolant

tubes is most significant, because future radiographic examinations may re-

veal whether the tubes have undergone any corrosive attack.

Bore, contour, 10 -1 and erosive wear in refractory-lined piping can beseen by means of gamma radiography. Figure 6 is a schematic diagram ofone type of refractory-lined transfer line that was radiographed. This itemwas radiographed before and after about 200 h of solids circulation. Figures 7and 8 are schematic diagrams showing the pre- and postcirculation conditions,

respectively, of the refractory in the Y sec.ion. Figures 9 and 10 are sche-mati: diagrams showing the condition of the refractory before and after solids

were circulated through the elbow section. As a result of these findings, it wasnecessary for Battelle personnel to modify and install a system that would re-duce the erosion rate.

Fig. 4. Radiograph of Section of Battelle' C ombustor Vsicl showingVoids beneath Vapor Barrie! and Orientation of a liangcr

13

Fig. 5. Radiograph of Section of Bi-Gas Gasifier Showing Void in Center of Film

SOLIDS FLOW TO BURNER

100 mm

SOLIDS FLOWFROM GASIFIER

AERATIONLINES

Fig. 6. Schematic Diagram of Refractory-lined Trans-fer Line at Battelle. Neg. No. MSD-65119.

36cm -

I

-- ae/

-i,

%

7 4

Fig. 7. Schematic Diagram of Y Section before Solids WereCirculated through System. Neg. No. MSI-65125.

14

I 7

LIE

I I 7I I 7

I I z

I I7

I 7

I I 77

I I

t' ~36 a ---

Fig. 8. Schematic Diagram of Y Section after Solids WereCirculated through System. Neg. No. MSD-65124.

LINES

Fig. 9. Schematic Diagram of Elbow before Solids WereCirculated through System. Neg. No. MSD453127.

15

Fig. 10

Schematic Diagram of ElbowShowing Refractory Erosion afterSolids Were Circulated throughSystem. Neg. No. MSD-65126.

Like most nondestructive tests, gamma radiography has its limitations.The vessel cross section shown in Fig. 1 is about at the limit of useful pene-tration for 60Co. Bore definition of refractory-lined pipe having a 51 -cm(20-in.) OD with a 10-cm (4-in.) bore was marginal. In spite of this, gammaradiography is a valid nondestructive test to detect changes in refractory-lined vessels and piping.

IO

\lthuulgh laboratory test" helpl( est. blish half-valuc layers for the

Ilor tmoln refractories iserl in (01l -( Onversin co mponent linings

Isee tle II). fied(1 ttsts establiShcd pru eclIres for I- situ gamm a rarli-,r2 }Iv. ' hese newly (lev loprl per ( res will help in flu re implem nta-

ti)n )f r n1 . I a r ii r)tL phy.

\.. 1 qi;)perit and Iield-implemnentltion ConsilertAtions

\ hile conduct tin14 fie l(1 radlio raphy a' the v( riots ( oa l-conve rsion

tet fat jlities . .\roI lne personnel have enco, t ered soi l difficulties that

shouldI be mentioned. Yiirst, the container that houses the Co source mustbe t ransported onto the stru -

weilh -1 .i - () io k2 (1)000-

S170) IL). A' e levat)r or hoistable to safely lift the weight

must be available. Second.

to genc'r".te panroramilc radIto-

raphs of equal clensities. a

hollow tube with II) nominally

should be inserted into the

center of the vessel and securedat the top flan"e, as shown inl- ig. I 1. to accommodate the

flexible tube containing theFCo source. This methodallows the source-to-film

: .11. VcseI Iiht erg 'd fromn XI- distancee to be maintained at

ii IIV II . [K I l:. K I i a onstant value l u (I ing theexposuI re. The film should

follow the contour of the vessel to ma intain the equal elistance desi red between

the source and the detector. 1-lexibl- assettes satisfy this requirement; theyshould be secured around the diameterI of a vessel (by tape, rope, or both).

I.ear figures and numbers are necessary for identification.

Ii

Fili types we hawe - used stc cessfnlly hive been ])If Pon '1 ype NI) '

anld F.astmlnan lKo(lak 1 ype A:\. The film is always used with O. I;A -m1111

(u. 1l -in.)-thick leal foil sc reens at the exposiire side anIIl back sile. '1he

SC reenS inc rease the phOtonraphic action on the film, largely by emitted

elect runs and paI rtl by the sec unrla ry ra(IiatiOn e ne ratedl in the leal; in

a(Ilition. they absorb s atered radiation.

Special penet riIeters shoul be fabricated} of the samne refrut to ry

material used1 in he lining of the oImponent to be raliographedl. If it is im-

practical to fabric' ate penet rIIneters I rum the mate rial being radiug raohedl,

a refra( tory material shul1I be < chosen

that has a clensity as close as possible

to the One IIunder going ra dio grphi(

testing. If there is ,, choice betwAeen

a hi gher - anl lower-(lensityv refra to rv

it is better tu choose the lItter betaiuse

the ( rlt 1 it- sen.it I \it y O1 the pelit-

tr tu et 'r 1un 1 Le ol the fi1 1 wol l then

be less than l.2.

l'en tr1mt r 1Oiund Isefl

i W I I" r 1 t 1r ,1 r ' dl. t set -eud s f )

\l h11 , thi( < !ness 1 1O .'t O1 the

ti)tal 1i1 i '.cie - (1 t ht' 'fri to r\- - st (t'l-( )S t't in l e s i' s 1 i t o' 101.

ref ri tory--tet ti n ss of pipin

l le rll~ t tlle l( t ' + )1 lilt' 1(+l ' 1- t ( I1.+ t()

the pentetr. t eter t!1! ( n . Ine

11111 of the !01 wt r il 1it-t-r 1):1 1the

ro ( s(: trI fi 1I1 i ill i ! (i+ +) . -

trast -t's itivity )f I'l'l t:'rmnIi t k'I'r

should h e placed on1 the 11i 1 sile of the o nimpOneit he I, i.spe tei. I 4 eti'it

of the penetramneter Ol the sou1r1 e tidie of ile (om'Iponenit \\)OI(1 re llt 1n

distorted image, be( ause the obiect (penet r.aineter- to-Him1 (istanc i. too

great. A penetratmiieter should be plat ed( on eat h fidni t11t is txposIe(.

B. Single -wall eadiog raphy

Planoramiic gaImtlla radiographsl are taket of reri, tory-lined Vessels

at the elevations of interest. 1'a11oramit radiographs ire taken by seth rinfilm entirely around the vessel in the manner shown in li'. I " . :\ Co sou rceof at least I.85 x Io O q () Ci) is inserted into a hollow to be to the desiredelevation and maintained for the duiiration of the exposiir(e. [at h film shOulIdbe identified at each radiographed elev.'ation. liltml ident ificat ion tan be madeas shown in Fig. ll. Vxposure times may vary from elevation to elevation,depending on the vessel-wall thickness, refractory thickness, and the absence

or presence of internal components.

18

Photograph of Gasifier Vessel

Showing Position of Film Cas-

settes Secured to Vessel

I. i

w} TOP VIEW OF

I IGA SIFIE R

C) GASIFIERF

m I\ FILM

60 CORALSOURCE E\

OU TSIDEOF

GASIFIER

Fig. 14. Proposed Film-identification Method for Panoramic Radi-ography of Refractory-lined Vessel. Neg. No. MSD-65118.

Laboratory experiments1 0 to detect the effect of moisture content in

the refractory on photographic density showed a density difference of 0.41between as-cast and cured KAOTAB refractories using the same exposuretime. Field tests of ALFRAX BI 57 refractory-radiographed before and afterrefractory curing indicated an exposure-time difference of about 50%. Re-fractory moisture content had no effect on image quality or sensitivity ineither instance.

19

One way to determine exposure time is to calculate the refractory

equivalence to steel and refer to a conventional 60Co exposure calculator.

As a rule of thumb for determining approximate refractory/steel equivalence

for high-alumina refractories, 7.6 cm (3 in.) of refractory is about equal to

2.54 cm (1 in.) of steel. Another method successfully used to determine ap-proximate exposure times for vessel walls is to take gamma readings at the

outer wall of the vessel at the precise location of the film after the source is

propelled into the hollow tube. The reading can be made with any suitable

gamma-survey instrument, such as a Victoreen Model 592B.

To calculate approximate exposure time, refer to Table III and locate

the type of film being used and the desired film density. The table indicatesthe total amount of radiation required to expose the film to that density. Forexample, suppose a reading taken at the wall of the vessel indicates a radiationlevel of 3.87 x 10-5 C/kg (150 mR/h). DuPont NDT 75 film is used, and thedesired density is 1.5. From Table III, we see that a total of 710 mR150 mR = 4.7 h.

TABLE III. Total Amount of 6Co Radiation (in roentgensa) Requiredto Yield Variuus Film Densities

Density

Film 1.0 1.5 2.0 2.5 3.0 4.0

GAF C 0.120 0.210 0.310 0.430 0.560 0.900DuPont 75 0.430 0.710 1.0 1.8 1.7 2.5GAF A 0.700 1.2 1.7 2.2 2.8 4.0EKC AA 1.0 1.7 2.3 3.0 3.7 5.1DuPont 55 1.9 1.9 4.1 5.2 6.3 8.8DuPont 55 1.2 3.8 2.5 3.2 4.0 5.7GAF B 2.7 8.1 6.0 7.5 9.3 13EKC M 5.4 10 11 13 16 2lGAF HD 6.9 12 13 17 20 27DuPont 45 7.9 19 16 20 24 33EKC R 12 25 31 36 45

aConversion factor: I roentgen = 2.58 x 104 C/kg.

To verify that the calculated exposure is correct, an extra (test)film should be placed behind the film that is in place. After about two-thirdsof the calculated exposure time has elapsed, retract the source to its originalcontainer, remove the test film carefully so as not to disturb the other film,and process it. If the processed-film density seems low, lower the sourceto its original position and continue the exposure to the calculated time. Ifthe film density is proper, the original film may be removed for processing.

C. Double-wall Radiography

In the radiography of refractory-lined piping to obtain the bore contour,a collimrated beam of radiation is directed at one side of the pipe and film issecured at the opposite side, 180' from the source side. Figure 15 is a sche-matic diagram showing the arrangement used for radiography of piping.

20

Figure 16 shows the collimated source in position to generate a radiograph.

Radiography is best performed during a plant shutdown period, after the pipinghas cooled. Piping can be radiographed at elevated temperatures [up to 260'C(500 F)] when the plant is in operation, if insulation is wrapped around the pipe

to protect the film and film cassette from heat.

REFRACTORY

BOREPIPE WAY

Fig. 15

Typical Arrangement for RadiographingRefractory-lined Piping to Obtain Bore

FILM Contour. Neg. No. MSD-65120.COLLIMATED

60 COBALTSOURCE

Fig. 16. Photograph of Collimator in Position to Generate Radiograph

The amount of insulation required depends on the surface temperatureof the piping to be tested. The amount of insulation is adequate when the surfaceagainst which the film is to be placed is just warm to the touch. However, thismethod is not recommended because it increases the object-to-film distanceby several centimeters and consequently degrades the image on the film.Vibrations in the system may also degrade the quality of the radiographicimage, and may make it difficult to place the film at the desired location andkeep it in place for the duration of the exposure.

21

Source-to-film distance may vary, depending on the diameter of thepipe and the area being exposed. Typically, the source-to-film distance mayrange from 1.2 to 1.8 m (4 to 6 ft). Exposure time is calculated and verifiedas described above for single-wall radiography.

D. Conclusions and Recommendations

Gamma radiography with 60Co has been shown to be a useful method

to inspect refractory-lined vessels and piping. We have demonstrated that

gamma radiography is capable of:

1. Imaging anchor orientations.

2. Recording density changes in the refractory caused by voids ordifferences in thickness or materials. Crack images 21.27 mm (0.05 in.)wide were discernible through nominally 23 cm (9 in.) of refractory. Voidimages as small as 6.3 mm (0.125 in.) can be seen through about 46 cm(18 in.) of refractory.

3. Imaging thin-walled coolant tubes. Thin-walled water-coolanttubes about 3.76 cm (1.5 in.) in diameter can be seen through nominally 46 cm(18 in.) of refractory.

4. Inspecting bore contour in refractory-lined piping.

5. Inspecting for proper installation of air-lift lines.

6. Showing air-lift-line blockage or damage.

7. Determining erosion rate of refractory.

Continued use of gamma radiography in coal-conversion systems maystimulate wider applications of the method that have been discussed.

Personnel at present and future coal-conversion plants should considerthe application of gamma radiography to critical areas where refractoryerosion may occur.

22

APPENDIX

Supplementary Information Related to Radioisotopic Sources

1. Radiographic Sources

a. Curie

The curie is a measure of the disintegration rate of a source:

1 Ci = 3.7 x 1010 Bq = 3.7 x 1010 disintegrations per second.

b. Half-life

The half-life, T, of a given radioisotope is the length of timered for the activity to decay to one-half its initial strength. Because

any radioactive isotope decays ex-

I I I I I I I I I I I | ponentially, it will require a definitetime to fall to any given fraction ofits initial strength. The manufacturer

furnishes decay curves with every

source purchased. Figure 17 is adecay chart for 6Co.

c. Half-value Layer

The half-value layer (hvl)is the thickness of a material thattransmits 50% of the radiation inci-dent upon it. Table II shows the half-value layers of some materials thatare common in coal-conversionsystems.

d. Gamma-ray Energy20 j

The energy of gamma

100 1 2 3 4 5 6 7 e 9 10 11 12 rays, expressed in thousands of elec-tron volts (keV) or millions of electron

5.3 10.6TIME (YEARS) volts (MeV), corresponds to that of

the maximum-energy, or hardest,

Fig. 17. Decay Chart for 6 0Co. X rays generated by an electronicNeg. No. MSD-65117. X-ray tube energized at the stated

potential. Since most of the X raysemitted by a tube are at about 40% of the maximum energy, gamma rays showcharacteristics similar to X rays of about twice the stated energy. Thus, thepenetrating ability of gamma rays from 6Co, with energies of 1.17 and1.33 MeV, is similar to that of X rays from a 3-MeV X-ray generator.

requi

100

90

80

F-zWWWa,

70

60

So

40

30

HALF LIFE

HALFLIFE

23

e. Specific Activity

The specific activity of an isotopic source, usually measured in

curies per gram of source material, is of importance to radiographers in

two ways. First, a high specific activity indicates that a source of a given

strength will be of smaller physical size and thus will tend to yield sharper

radiographs. Second, less self-absorption of radiation will take place in a

small source.

f. Roentgen

The roentgen (R), a unit of radiation intensity, is defined as that

quantity of radiation for which the associated corpuscular emission produces,

in 1 cm 3 of dry air at 00C and 760 mm pressure, ions carrying one electro-

static unit of electricity of either sign.

g. Gamma-ray Intensity

Gamma-ray intensity is measured in roentgen per hour (R/h).A useful output number to associate with a radioactive source is (R/h)/Ci at

a distance of 1 m (RHM/curie), a measure of radiation emission over a given

period of time at a fixed distance. The activity (amount of radioactive material)

of a gamma-ray source determines the intensity of its radiation.

2. Fundamentals of Radiography

To be examined by radiography, an object must be placed in the path

of an X-ray (or gamma-ray) beam, and the intensities of the radiation passing

through different parts of the specimen must be compared. The most common

method for accomplishing this is to let the ray strike a recording medium,such as a photographic film, so that the blackening of the film after processingbears some relation to the radiation intensities. The resultant film is calleda radiograph.

The image on the film is formed by X or gamma rays traveling instraight lines from the source through the object to the film. Figure 18 is aschematic diagram showing the fundamentals of a radiographic exposure.This geometric image formation is similar to shadow formation with visiblelight, and the sharpness of the image on the film depends on the area of theradiation source and on the source-to-film distance. A small-diametersource, i.e., a small-diamcter X-ray tube focus or a small-dimensionedgamma-ray source, will produce sharp images; the important dimensionsare the effective length and breadth of the focus, measured in a plane parallelto the plane of the film.

- GAMMA RAYSOURCE

III'~ll \

III

li II \II Il l \

ll \

I I(ISI I Ii

I OBJECT

S I I I

Fig. 18

Schematic Diagram Showing Fundamentalsof Radiographic Exposure. The dark regionof the film represents the more penetrablepart of the object, the light regions the moreopaque. Neg. No. MSD-65116.

-FILM

It has been demonstrated that, from an image-sharpness point of view,

a large-area X-ray or gamma-ray focus can be compensated for by using alonger source-to-film distance. However, the intensity of the radiation at theplane of the recording media (film) varies inversely as the square of the dis-

tance between the source of radiation and the film. This is known as theinverse-square law. The inverse-square law can be expressed algebraicallyas

Ii D tIz Di

where I1 and IZ are the intensities at the distances Dl and DZ, respectively.As the distance is increased, the exposure time that the film requires toproduce a given effect increases rapidly. If the distance is doubled, four timesthe exposure time is necessary, and the exposure time may become too longto be practical.

3. Radiation Safety

The degree of safety with which a radiation device can be used dependsupon the intelligence and judgment of the person who uses it. If appropriateprecaurione are taken, radioactive materials used in industrial radiographycan be ised as safely as toxic materials or electricity, which are common toindustrial processes. The primary potential hazard from radiographic sourcescomes from exposure of personnel to radiation emitted by the sources. Gamma

24

25

radiation, like electricity, is to be respected more than feared. The three

basic principles involved in controlling exposure of the body to gamma radia-

tion are time, distance, and shielding.

a. Time

The total radiation exposure received by an individual in a field

of radiation depends upon the length of time he stays there. A person re-

maining in a given field of radiation for 5 min would receive only one-half

as much exposure as he would in 10 min.

b. Distance

The farther from a radiographic source a person can work, the

lower will be his exposure for any given period of time. The exposure rate

from a radioactive source decreases with distance in the same manner that

the intensity of light decreases as a person moves farther from the source

of light; i.e., the exposure rate varies inversely with the square of the distance

from the source (inverse-square law, as shown previously).

c. Shielding

The use of shielding materials provides an excellent means for

controlling personnel exposure while performing radiography. Materials

commonly used to shield gamma radiation are concrete, lead, iron, and steel.Adequate shielding will probably not be available during exposures in fieldoperations, because of the great amounts that would be necessary. To com-pensate for this, an area should be roped off around the location of the radio-active source, and personnel should be prohibited from entering this areaexcept to put the source in position or return it to its container. Radiationwarning signs should be posted to warn personnel to stay out of the area.

The radiation level outside the roped-off area should not exceed5.16 x 10-7 C/kg-h (2 mR/h).

4. Measuring and Monitoring Devices

Safe operating conditions must be maintained while radiographs aregenerated in the field. The operator using a radioactive source should there-fore be familiar with radiation-measuring and -monitoring devices.

Three general types of radiation-monitoring devices are used for fieldradiography. One type consists of a small penlike ionization chamber. Givenan initial electrostatic charge, it discharges in proportion to the amount ofradiation received. Direct-reading chambers (dosimeters) indicate, on anelectrometer indicator in the chamber, the amount of radiation that has beenreceived.

26

A second type of radiation monitor uses a large ionization chamberin conjunction with an electronic rate meter. This instrument reads theradiation intensity being received at a given location at the specific timethat the instrument is in operation, independent of the time of exposure.These instruments (gamma-survey meters) are read by the deflection on ameter, which is calibrated directly in milliroentgens per hour. The gamma-survey meter is most useful for posting the areas of radiation hazard andfor determining the minimum safe distance between personnel and the ex-posure area.

A third type of radiation-monitoring device is the film badge. Thisconsists of a small film holder equipped with thin filters for insertion ofspecial film sensitive to X and gamma radiation. After a period of time(often a month), the films are processed and the resultant radiographic filmdensity through the various thicknesses of filter is read with a densitometer.By comparing the resultant density on the film, an individual can determinethe amount of radiation he has received.

The operator of the exposure device and all personnel in the exposurearea must wear film badges and dosimeters, and a properly calibrated gammasurvey meter must be readily available.

27

ACKNOWLEDGMENTS

I wish to acknowledge the close cooperation of Mr. John Miles andMr. John Byron of Phillips Petroleum (Bi-Gas), Mr. Bob Adams of Battelle,Mr. Clark Abrams of Gamma Field Radiographic Facility, and Mr. RobertVogt, formerly of ANL. I also wish to thank Drs. K. J. Reimann andW. A. Ellingson for valuable discussions and help in the preparation of this

report.

REFERENCES

1. Radiography in Modern Industry, Eastman Kodak Company, Rochester, N.Y.(1969).

2. R. Halmshaw, Ed., Physics of Industrial Radiology, Heywood Books, London.1966).

3. 3. F. Shackelford, Nondestructzve Testing of Ceramics--Nomograph forX- and ka-m-Radiography, Ceram. Bull. 55, 210 (1976).

4. J. J. Borbas, R. C. Radfield, and E. Moscher, Density Determination ofRefractories by Measurement of Gcawa Radiation Absorption, J. Am. Ceram.Soc. 50, 421-424 (1977).

5. Materials Science Division Coal Technology Second Quarterly Report,January-March 1975, ANL-75-XX-2.

6. Materials Science Division Coal Technology Third Quarterly Report,April-June 1975, ANL-75-XX-3.

7. Materials Science Division Coal Technology Fourth Quarterly Report,July-September 1975, ANL-76-7 (Mar 2, 1976).

8. Materials Science Division Coal Technology Fifth Quarterly Report,October-December 1975, ANL-76-22 (Apr 27, 1976).

9. Materials Science Division Coal Technology Sixth Quarterly Report,January-March 1976, ANL-76-60 (June 14, 1976).

10. Materials Science Division Coal Technology Seventh Quarterly Report,April-June 1976, ANL-76-111 (Nov 23, 1976).

11. Materials Science Division Coal Technology Eighth Quarterly Report,July-September 1976, ANL-76-125 (Feb 28, 1977).

12. Materials Science Division Coal Technology Ninth Quarterly Report,October-December 1976, ANL-77-5 (May 16, 1977).